I have now replaced the cable between the slnb and the explorer. I also routed part of it differently, the previous cable was running parallel to the mains 220 vac supply cable in the wall, probably causing the low signal strength on tuner 1.

After some fine tuning of the dish, my signal levels are now at 100/100 for tuner 1 across all channels except ch.111 and ch.116 where the levels are at 100 strength and 61 quality.

Tuner 3 is at 88/80. Not sure if there is any more that I can do to improve tuner 3 signals?